[Congenital hip dysplasia in Ostfold 1990-96].
BACKGROUND: The focus in this paper is on the prevalence, risk factors and treatment of developmental dysplasia of the hip (DDH), before and after introduction of sonographic examination in 1993. MATERIAL AND METHODS: 1,469 (8.2%) infants were followed up because of clinical findings or risk factors (542 with X-ray and 927 with sonographic examination). RESULTS: The overall prevalence of DDH was 1.14%; 0.92% in neonates and 0.22% as late DDH. The prevalence of late DDH ranged from 0.07% to 0.52% (p < 0.01) with peaks in spring and autumn. The following changes occurred when sonography was introduced: Newborn DDH decreased from 1.06 to 0.77% (p < 0.05), late DDH decreased from 0.26 to 0.19% (not significant), and treatment duration decreased from 6.2 months (SD 1.4) to 4.2 months (SD 1.3)(p < 0.01). 56 of 198 infants with clinical findings (28%) were confirmed to have sonographic DDH (p < 0.01). Previous risk factors were confirmed. Mothers of infants with late DDH had higher pre-pregnancy weight, 63 kg (SD 11) vs 58.5 kg (SD 7.8), p < 0.02) and lower weight gain in the last trimester, (4.2 kg (SD 2.2) vs 6.6 kg (SD 2.7; p < 0.001), compared to a reference population. INTERPRETATION: Sonography has reduced treatment rate and duration of DDH.